For formation of a print employing a thermal transfer mode, a thermal transfer image-receiving sheet which is provided with a receiving layer on a substrate (e.g., Patent Literature 1) or an intermediate transfer medium in which a transfer layer in which a peeling layer and a receiving layer are layered in this order on a substrate is provided peelably from the substrate (e.g., Patent Literature 2) is employed. According to the thermal transfer image-receiving sheet that has been proposed in Patent Literature 1, a print can be obtained by forming a thermally transferable image on the receiving layer of the thermal transfer image-receiving sheet by means of a thermal transfer sheet having a colorant layer. According to the intermediate transfer medium that has been proposed in Patent Literature 2, a print where a thermally transferable image has been formed on an optional transfer receiving article can be obtained by forming the thermally transferable image on the receiving layer of the intermediate transfer medium by means of a thermal transfer sheet having a colorant layer, and then transferring the transfer layer which includes this receiving layer onto the optional transfer receiving article. Particularly, an intermediate transfer medium is particularly preferably used for transfer receiving articles onto which colorants are less likely to transfer and thus which cannot form a high-quality image directly thereon, transfer receiving articles which easily fuse with a colorant layer on thermal transfer and the like.
Improvement of the durability of an image formed product is also carried out by transferring a transferable protective layer onto the image formed product where a thermally transferable image has been formed by means of a protective layer transfer sheet in which a transferable protective layer is provided on a substrate (e.g., Patent Literature 3).
Incidentally, depending on the type of the print formed by means of an intermediate transfer medium, it may be necessary to leave a certain region untreated, for instance, regions allocated for an IC chip, a magnetic strip, a transmitting and receiving antenna unit, or a signature portion. Specifically, in the stage before the transfer layer is transferred onto a transfer receiving article, it may be necessary to remove a portion of the transfer layer corresponding to a region allocated for an IC chip, a magnetic strip, a transmitting and receiving antenna unit, a signature portion or the like. It also may be desired to selectively transfer a transferable protective layer onto an image formed product.
Under such circumstances, some attempts have been made, wherein, by using a thermal transfer sheet in which a peel-off layer is provided on one surface of a substrate, in the stage before the transfer layer of an intermediate transfer medium is transferred onto a transfer receiving article, a portion of the transfer layer, for example, a region of the transfer layer which is not desired to be transferred onto the transfer receiving article is removed by means of the peel-off layer in advance (it may be also referred to as “peeled off”). For example, Patent Literature 4 proposes a method in which, after the peel-off layer of a thermal transfer sheet and the transfer layer of an intermediate transfer medium are superimposed so as to be brought into contact to each other, an energy is applied to the other surface of the substrate of the heat transfer sheet, and the transfer layer corresponding to the region to which the energy has been applied is removed by means of the peel-off layer.
As one of problems that may be caused when a portion of the transfer layer of the intermediate transfer medium or of the transferable protective layer of the protective layer transfer sheet is removed by means of the peel-off layer of the above-described thermal transfer sheet, a problem in which the peel-off layer, which naturally should remain together with the transfer layer or the transferable protective layer that has been removed on the side of the thermal transfer sheet, transfers to the side of the intermediate transfer medium or the protective layer transfer sheet (so called reverse transfer of the peel-off layer) or a problem in which the transfer layer, which should be naturally removed by means of the peel-off layer, remains on the side of the intermediate transfer medium or the protective layer transfer sheet can be included. These problems are likely to occur in the case where adhesiveness between the substrate and the peel-off layer (it may be also referred to as an adhesive property) is low. Under such circumstances, for example, in Patent Literature 4 described above, an embodiment in which adhesiveness between the substrate and the peel-off layer has been improved by using a substrate subjected to easily-adhesive treatment is proposed although no attention is paid to the peel-off property of the transfer layer or the transferable protective layer.
However, responding to a recent demand for accelerating printers, the energy applied to the thermal transfer sheet tends to increase when the transfer layer of an intermediate transfer medium or the transferable protective layer of a protective layer transfer sheet is removed by means of a peel-off layer. In the case where, as the transfer layer of the intermediate transfer medium or the transferable protective layer of the protective layer transfer sheet, a layer having high durability, for example, a thick transfer layer or transferable protective layer is used, it becomes difficult to remove the transfer layer or the transferable protective layer unless the energy to be applied to the thermal transfer sheet is increased. As for thermal transfer sheets having a peel-off layer proposed up to now, the measure in the case where the energy applied to the thermal transfer sheet is increased is not sufficient on removal of a portion of the transfer layer or the transferable protective layer. The peel-off property of the transfer layer of the intermediate transfer medium or the transferable protective layer of the protective layer transfer sheet when a high energy is applied to the thermal transfer sheet leaves room for improvement.